As packaging containers, there have recently been used various kinds of plastic containers, because of their advantages, for instance, their light-weight characteristics, excellent transparency and their easy moldability.
However, the plastic containers are insufficient in the oxygen-barrier properties as compared with those observed for the metallic and glass containers and accordingly, they suffer from problems such that the contents packaged therein are degenerated and that the flavor of the contents are significantly deteriorated.
To solve such a problem associated with these plastic containers, the plastic containers have been so designed that they have walls prepared using multi-layer structures each having at least one layer of a resin having oxygen-barrier properties such as an ethylene-vinyl alcohol copolymer. In addition, there has been proposed a container provided with an oxygen-absorbing layer in order to remove the oxygen remaining in the container and the external oxygen gas possibly entering into the container. As oxygen gas-absorbers (deoxidizing agents) used in the oxygen-absorbing layer, there have been known, for instance, those each containing an oxygen scavenger consisting of, for instance, an ethylenically unsaturated hydrocarbon and a transition metal catalyst (see, for instance, Patent Document Nos. 1 to 3 specified below).
According to the method which makes use of such an oxygen scavenger consisting of an ethylenically unsaturated hydrocarbon and a transition metal catalyst, the ethylenically unsaturated hydrocarbon per se absorbs oxygen gas to thus ensure the oxygen-barrier properties of the scavenger. However, this method suffers from a problem such that the hydrocarbon material would generate low molecular weight decomposition products when the material absorbs oxygen gas and the decomposition products may adversely affect the taste and palatability as well as the flavor of the contents. To solve the foregoing problem, there has been disclosed a method for adding a neutralizing agent reactive with an acid, an alcohol or an aldehyde and more specifically, an inorganic base or an organic amine, while taking notice of the decomposition products (see Patent Document No. 4 specified below).
However, it has been found that the following problem arises: when using the container made of the known plastic multi-layer structure having oxygen-barrier properties in an atmosphere having a high humidity, the structure generates an increased amount of decomposition products formed through the oxidation thereof and this accordingly adversely affects, for instance, the taste of the contents, to a considerable extent. It has been found that the problem becomes more serious when storing the contents over a long time period under high temperature and high humidity conditions during the summer season and using such a container for packaging contents each having a high water content, in particular, liquid foods or pharmaceuticals.    Patent Document 1: Japanese Un-Examined Patent Publication (JP Kokai) 2001-39475    Patent Document 2: JP Kokai Hei 5-115776    Patent Document 3: JP Kokai Hei 8-502306    Patent Document 4: JP Kokai 2000-506087